U.S. patent application number 10/445839 was filed with the patent office on 2003-12-11 for thermal fixing device and image forming device provided with the same.
This patent application is currently assigned to Brother Kogyo Kabushiki Kaisha. Invention is credited to Yokoi, Katsuyuki.
Application Number | 20030227533 10/445839 |
Document ID | / |
Family ID | 29706818 |
Filed Date | 2003-12-11 |
United States Patent
Application |
20030227533 |
Kind Code |
A1 |
Yokoi, Katsuyuki |
December 11, 2003 |
Thermal fixing device and image forming device provided with the
same
Abstract
A thermal fixing device is provided in an image forming device
having a main casing. The thermal fixing device includes a thermal
fixing unit provided with a heat roller and a pressure roller for
heatingly fixing a visible image onto a sheet, and a temperature
sensor unit for detecting a temperature of the thermal fixing unit.
The temperature sensor unit is mounted to the main casing, and the
thermal fixing unit is detachably mounted to the temperature sensor
unit.
Inventors: |
Yokoi, Katsuyuki;
(Iwakura-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Brother Kogyo Kabushiki
Kaisha
Nagoya-shi
JP
|
Family ID: |
29706818 |
Appl. No.: |
10/445839 |
Filed: |
May 28, 2003 |
Current U.S.
Class: |
347/156 ;
347/158 |
Current CPC
Class: |
G03G 21/1685 20130101;
G03G 15/2053 20130101; B41J 11/002 20130101 |
Class at
Publication: |
347/156 ;
347/158 |
International
Class: |
B41J 002/385 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 2002 |
JP |
2002-169176 |
Claims
What is claimed is:
1. An image forming device comprising: a main casing; and a thermal
fixing device comprising a thermal fixing unit that heatingly fixes
a visible image onto an image recording medium and a temperature
sensor unit that detects a temperature of the thermal fixing unit,
the temperature sensor unit being mounted to the main casing, and
the thermal fixing unit being detachably mounted to the main
casing.
2. The image forming device as claimed in claim 1, wherein the
thermal fixing unit is detachably mounted to the temperature sensor
unit.
3. The image forming device as claimed in claim 1, wherein the main
casing defines therein an attachment/detachment path for the
thermal fixing unit, the temperature sensor unit being mounted to
the main casing at a position offset from the attachment/detachment
path.
4. The image forming device as claimed in claim 3, wherein the
temperature sensor unit is positioned in front of the
attachment/detachment path of the thermal fixing unit.
5. The image forming device as claimed in claim 4, wherein the
temperature sensor unit comprises a temperature sensor having a
detection window opened to a rear side of the temperature sensor
unit; and wherein the thermal fixing unit comprises a fixing unit
casing formed with a receiving hole through which the temperature
sensor is positioned.
6. The image forming device as claimed in claim 1, wherein the
temperature sensor unit is detachable from the main casing.
7. The image forming device as claimed in claim 1, wherein the
temperature sensor unit comprises a temperature sensor, and wherein
the thermal fixing device further comprising a positioning section
for positioning the temperature sensor with respect to the thermal
fixing unit.
8. The image forming device as claimed in claim 7, wherein the
positioning section comprises a positioning pin protruding from one
of the temperature sensor unit and the thermal fixing unit, and a
positioning recess engageable with the positioning pin and formed
at remaining one of the thermal fixing unit and the temperature
sensor unit.
9. The image forming device as claimed in claim 8, wherein the
positioning section further comprises a biasing member that bias
one of the positioning pin and the positioning recess toward
remaining one of the corresponding positioning recess and the
positioning pin.
10. The image forming device as claimed in claim 8, wherein the
positioning pin comprises three positioning pins arrayed offset
from each other, and wherein the positioning recess comprises
associated three positioning recesses arrayed offset from each
other, and positioning recess being engaged with each associated
positioning pin.
11. The image forming device as claimed in claim 8, wherein the
temperature sensor comprises a non-contact type temperature
sensor.
12. The image forming device as claimed in claim 11, wherein the
non-contact type temperature sensor comprises a thermopile.
13. The image forming device as claimed in claim 1, wherein the
thermal fixing unit comprises a heating component, and a pressure
component in pressure contact with the heating component, the
temperature sensor unit detecting a surface temperature of the
heating component.
14. The image forming device as claimed in claim 1, wherein the
temperature sensor unit comprises a temperature sensor having a
detection window, and wherein the thermal fixing device further
comprises a protecting section for covering the detection window
when the thermal fixing unit is detached from the temperature
sensor unit.
15. The image forming device as claimed in claim 1, wherein the
temperature sensor unit comprises a temperature sensor having a
detection window, and wherein the thermal fixing device further
comprises a protective film positioned to cover the detection
window.
16. The image forming device as claimed in claim 7, wherein the
temperature sensor unit further comprises a stationary section
mounted on the main frame, the positioning section being supported
to the stationary section and movable with respect to the
stationary section in accordance with an abutment with the thermal
fixing unit, a position of the temperature sensor being fixed upon
abutment of the positioning section with the thermal fixing
unit.
17. The image forming device as claimed in claim 16, wherein the
thermal fixing unit comprises a fixing unit casing, and wherein the
positioning section comprises: a base plate movable with respect to
the stationary section; a positioning pin protruding from one of
the base plate and the fixing unit casing; and a positioning recess
engageable with the positioning pin and formed at remaining one of
the fixing unit casing and the base plate.
18. The image forming device as claimed in claim 17, wherein the
positioning pin comprises three positioning pins protruding from
the base plate, and the positioning recess comprises three
positioning recesses formed at the fixing unit casing, positioning
pins having protruding length equal to each other.
19. The image forming device as claimed in claim 18, wherein the
stationary section comprises: a support plate detachably fixed to
the main casing; a temperature sensing plate fixed to the support
plate; and engagement legs extending from the temperature sensing
plate, each engagement legs having a free end provided with a
locking pawl engageable with the base plate; and wherein the
positioning section further comprises: three spring securing
portions protruding from the base plate and each extending in line
with each positioning pin and protruding in a direction opposite to
each positioning pin; and three biasing spring interposed between
each spring securing portion and the stationary section for urging
the base plate toward the locking pawl.
20. A thermal fixing device comprising: a thermal fixing unit that
heatingly fixes a visible image onto an image recording medium; and
a temperature sensor unit that detects a temperature of the thermal
fixing unit, the thermal fixing unit being detachably mounted to
the temperature sensor unit.
21. The thermal fixing device as claimed in claim 20, wherein the
thermal fixing unit is attached to and detached from the
temperature sensor unit in an attachment/detachment direction; and
wherein the temperature sensor unit comprises a temperature sensor
having a detection window open toward the attachment detachment
direction; and wherein the thermal fixing unit comprises a fixing
unit casing formed with a receiving hole through which the
temperature sensor is positioned.
22. The thermal fixing device as claimed in claim 20, wherein the
thermal fixing unit is attached to and detached from the
temperature sensor unit in an attachment/detachment direction; and
wherein the temperature sensor unit comprises a temperature sensor;
and the thermal fixing device further comprising a positioning
section for positioning the temperature sensor with respect to the
thermal fixing unit.
23. The thermal fixing device as claimed in claim 22, wherein the
positioning section comprises a positioning pin protruding from one
of the temperature sensor unit and the thermal fixing unit, and a
positioning recess engageable with the positioning pin and formed
at remaining one of the thermal fixing unit and the temperature
sensor unit.
24. The thermal fixing device as claimed in claim 23, wherein the
positioning section further comprises a biasing member that bias
one of the positioning pin and the positioning recess toward
remaining one of the corresponding positioning recess and the
positioning pin.
25. The thermal fixing device as claimed in claim 23, wherein the
positioning pin comprises three positioning pins arrayed offset
from each other, and wherein the positioning recess comprises
associated three positioning recesses arrayed offset from each
other, each positioning recess being engaged with each associated
positioning pin.
26. The thermal fixing device as claimed in claim 23, wherein the
temperature sensor comprises a non-contact type temperature
sensor.
27. The thermal fixing device as claimed in claim 26, wherein the
non-contact type temperature sensor comprises a thermopile.
28. The thermal fixing device as claimed in claim 20, wherein the
thermal fixing unit comprises a heating component, and a pressure
component in pressure contact with the heating component, the
temperature sensor unit detecting a surface temperature of the
heating component.
29. The thermal fixing device as claimed in claim 20, wherein the
temperature sensor unit comprises a temperature sensor having a
detection window, and the device further comprising a protecting
section for covering the detection window when the thermal fixing
unit is detached from the temperature sensor unit.
30. The thermal fixing device as claimed in claim 20, wherein the
temperature sensor unit comprises a temperature sensor having a
detection window, and the device further comprising a protective
film positioned to cover the detection window.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a thermal fixing device and
an image forming device provided with the fixing device.
[0002] In an image forming device such as a laser printer, a
thermal fixing device including a heat roller and a pressure roller
is provided for thermally fixing a toner image onto a sheet. In the
thermal fixing device, the toner image which has been transferred
onto the sheet is thermally fixed to the sheet when the sheet
passes through a nip between the heat roller and the pressure
roller.
[0003] Generally, the heat roller installs therein a heater such as
a halogen lamp, and a temperature sensor is provided for detecting
a surface temperature of the heat roller. The fixing temperature
can be maintained at a constant temperature by ON/OFF control to
the heater based on the detection of the surface temperature by the
temperature sensor.
[0004] Known as the temperature sensor are a contact type sensor
such as a thermistor which is in direct contact with the heat
roller and a non-contact type sensor such as an infrared radiation
sensor which is out of contact from the heat roller. The
non-contact type sensors have been widely used in the thermal
fixing device because the heat roller can be protected against
injury for a expanded duration due to out of contact from the
sensor.
[0005] Conventionally, the temperature sensor has been provided in
the thermal fixing device together with the heat roller and the
pressure roller, because the temperature sensor must be in direct
contact with the heat roller in case of the contact type sensor, or
must be precisely set and oriented with respect to the heat roller
in case of the noncontact type sensor. Therefore, the temperature
sensor is attached to or detached from a main casing of the image
forming device when the thermal fixing device is replaced by a new
thermal fixing device.
[0006] In this case, the heat roller and the pressure roller must
be frequently replaced by new rollers due to frictional wear as a
result of pressure contact with each other, whereas the temperature
sensor and particularly the non contact type sensor needs not be
replaced frequently, because the latter can provide a prolonged
service life because of out of contact from the heat roller.
Therefore, in the conventional arrangement, frequent exchange of
the thermal fixing device is not economical in terms of the
sensor.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to overcome the
above-described problems and to provide an improved thermal fixing
device capable of only replacing a thermal fixing unit with a new
thermal fixing unit while a temperature sensor unit is still
installing in a main casing of an image forming device, thereby
avoiding wasteful use of the temperature sensor unit.
[0008] Another object of the present invention is to provide an
image forming device provided with such improved thermal fixing
device. These and other objects of the present invention will be
attained by an image forming device including a main casing, and an
improved thermal fixing device. The fixing device includes a
thermal fixing unit that heatingly fixes a visible image onto an
image recording medium and a temperature sensor unit that detects a
temperature of the thermal fixing unit. The temperature sensor unit
is mounted to the main casing, and the thermal fixing unit is
detachably mounted to the main casing.
[0009] In another aspect of the invention, there is provided a
thermal fixing device including the thermal fixing unit and the
temperature sensor unit. The thermal fixing unit is detachably
mounted to the temperature sensor unit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] In the drawings:
[0011] FIG. 1 is a schematic side view showing an internal
arrangement of a laser printer according to a first embodiment of
the present invention, and showing a state in which a thermal
fixing unit is assembled in a main casing while closing a rear
cover;
[0012] FIG. 2 is a schematic side view showing the internal
arrangement of the laser printer according to the embodiment, and
showing a state in which the thermal fixing unit is being detached
from the main casing while opening the rear cover;
[0013] FIG. 3 is a schematic perspective view showing essential
portions of the thermal fixing unit and a temperature sensor unit
according to the first embodiment of the present invention;
[0014] FIG. 4 is a cross-sectional view showing a casing of the
thermal fixing unit and a temperature sensing section of the
temperature sensor unit according to the first embodiment, and
showing a state where the thermal fixing unit is assembled to the
main casing;
[0015] FIG. 5 is a cross-sectional view showing the casing of the
thermal fixing unit and the temperature sensing section according
to the first embodiment, and showing a state where the thermal
fixing unit is detaching from the main casing;
[0016] FIG. 6 is a front view showing the temperature sensing
section according to the first embodiment;
[0017] FIG. 7 is a cross-sectional view showing a temperature
sensing section according to a second embodiment of the present
invention;
[0018] FIG. 8 is a cross-sectional view showing a temperature
sensing section according to a third embodiment of the present
invention; and
[0019] FIG. 9 is a front view showing a temperature sensing section
according to a fourth embodiment of the present invention;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] An image forming device according to a first embodiment of
the present invention will be described with reference to FIGS. 1
through 6. The embodiment pertains to a laser printer.
[0021] In FIG. 1, a laser printer 1 includes a main casing 2 in
which a feeder unit 4 for supplying a sheet 3 and an image forming
unit 5 for forming image on the sheet 3 are disposed. The feeder
unit 4 includes a sheet supply tray 6, a sheet supply roller 7, a
register roller 8 and a register sensor 31. The sheet supply tray 6
is detachably installed at a bottom of the main casing 2. The sheet
supply roller 7 is disposed above an outlet end of the sheet supply
tray 6. The register roller 8 is disposed downstream of the sheet
supply roller 7 in a sheet feeding direction. The register sensor
31 is disposed immediately upstream of the register roller 8.
[0022] The sheet supply tray 6 accumulates therein a stack of cut
sheets 3, and an uppermost sheet 3 of the sheet stack is supplied
toward the register roller 8 by the rotation of the sheet supply
roller 7. The register roller 8 includes a pair of rollers for
adjusting orientation of the sheet and then feeding the sheet to
the image forming unit 5. The register sensor 31 has an actuator
which is rendered ON upon abutment of a leading edge of the sheet
3, and is rendered OFF in case of non abutment of the leading edge.
The ON/OFF signals of the actuator can detect the feeding of the
sheet 3.
[0023] The image forming unit 5 includes a scanner unit 9, a
process device 10, and a thermal fixing device 11. The scanner unit
9 is positioned at an upper area within the main casing 2 and
includes a reflection mirror 9a, a laser emitting section (not
shown), a polygon mirror(not shown), and a plurality of lenses (not
shown). Laser beam is emitted based on image data from the laser
emitting section and is scanningly irradiated at high speed onto a
surface of a photosensitive drum 13 described later of the process
device 10 through the polygon mirror, the lenses, and the
reflection mirror 9a.
[0024] The process device 10 is disposed below the scanner unit 9
and includes a developing cartridge 12, the photosensitive drum 13,
a scorotoron charger 14, a transfer roller 15 and a drum cleaning
section 16. The developing cartridge 12 is detachably mounted on
the main casing 2 and includes a developing roller 17, a toner
thickness regulation blade (not shown), a toner supply roller(not
shown) and a toner container(not shown). A developing bias voltage
is applied to the developing roller 17. The photosensitive drum 13
is disposed beside the developing roller 17 in contact therewith,
and is rotatable in a direction indicated by an arrow in FIG.
1.
[0025] The scorotoron charger 14 is disposed above and spaced away
from the photosensitive drum 13 by a predetermined distance. The
charger 14 is of a positively charging type and includes a tungsten
wire for generating a corona discharge in order to uniformly charge
the surface of the photosensitive drum 13 with a positive
porosity.
[0026] The toner container contains generally spherical
polymerization toner as a developing agent. The toner is a
non-magnetized single component type toner and is positively
chargeable. The toner is supplied to the developing roller 17 upon
rotation of the toner supply roller, and a thin toner layer with a
uniform thickness can be formed over the surface of the developing
roller 17 by the toner thickness regulation blade. On the other
hand, the surface of the photosensitive drum 13 is uniformly
positively charged by the scorotoron charger 14 in accordance with
the rotation of the photosensitive drum 13, and is then, the
surface of the photosensitive drum 13 is exposed to scanning laser
beam from the scanner unit 9, so that an electrostatic latent image
can be formed on the surface of the photosensitive drum 13 based on
the image data. An electric potential at the irradiated area with
the laser beam becomes lower than that of the remaining area of the
surface of the photosensitive drum 13 which has been uniformly
positively charged. Then, by the rotation of the developing roller
17, a visible toner image is formed on the photosensitive drum 13
corresponding to the electrostatic latent image.
[0027] The transfer roller 15 is rotatably disposed immediately
below the photosensitive drum 13. The transfer roller 15 is driven
by the rotation of the photosensitive drum 13, and is applied with
a transfer bias during transfer of the toner image from the
photosensitive drum 13 to the sheet 3 when the sheet 3 passes
between the photosensitive drum 13 and the transfer roller 15.
[0028] The drum cleaning section 16 is positioned downstream of the
transfer roller 15 and upstream of the scorotoron charger 14 in the
rotational direction of the photosensitive drum 13. The drum
cleaning section 16 includes a drum cleaning roller 18, a secondary
cleaning roller 19, a cleaning blade 20 and a waste toner tank 21.
The drum cleaning roller 18 is in rolling contact with the
photosensitive drum 13, and has an outer peripheral surface region
formed with an electrically conductive elastic material. The drum
cleaning roller 18 is applied with a bias voltage with respect to
the photosensitive drum 13.
[0029] The secondary cleaning roller 19 is disposed downstream of
the photosensitive drum 13 in the rotational direction of the drum
cleaning roller 18, and is in rolling contact with the drum
cleaning roller 18 at a position opposite to the photosensitive
drum 13 with respect to the drum cleaning roller 18. The secondary
cleaning roller 19 is made from a metal, and is applied with a bias
voltage with respect to the drum cleaning roller 18.
[0030] The cleaning blade 20 is disposed downstream of the drum
cleaning roller 18 in the rotational direction of the secondary
cleaning roller 19, and is in sliding contact with the secondary
cleaning roller 19 at a position opposite to the drum cleaning
roller 18 with respect to the secondary cleaning roller 19. The
cleaning blade 20 includes a thin plate like scraper blade for
scraping off the toner from the surface of the secondary cleaning
roller 19.
[0031] Toner remaining on the surface of the photosensitive drum 13
after toner transfer onto the sheet 3 is electrically trapped by
the drum cleaning roller 18, when the remaining toner is brought
into confrontation with the drum cleaning roller 18 by the rotation
of the photosensitive drum 13. The trapped toner is then
electrically trapped by the secondary cleaning roller 19 when the
trapped toner on the drum cleaning roller 18 is brought into
confrontation with the secondary cleaning roller 19 by the rotation
of the drum cleaning roller 18. Then, the trapped toner on the
secondary cleaning roller 19 is scraped off by the cleaning blade
20 and collected into the waste toner tank 21.
[0032] The thermal fixing device 11 is positioned beside and
downstream of the process device 10, and includes a thermal fixing
unit 32 and a temperature sensor unit 35. The thermal fixing unit
32 is provided detachably from the main casing 2, whereas the
temperature sensor unit 35 is stationarily disposed in the main
casing 2. The thermal fixing unit 32 can be separated from the
temperature sensor unit 35. Incidentally, in the following
description, a side of the developing cartridge 12, and a side of
the thermal fixing device 11 will be referred to as a front side
and a rear side, respectively.
[0033] The thermal fixing unit 32 is positioned behind the
temperature sensor unit 35, and includes a casing 33, a heat roller
22, a pressure roller 23 those disposed in the casing 33, and a
pair of transport rollers 25 disposed at an outer rear face of the
casing 33.
[0034] The casing 33 is of a box shape elongated in a widthwise
direction of the sheet 3, i.e., in the direction perpendicular to
the sheet feeding direction as shown in FIG. 3. The casing 33 has a
front wall 33a formed with a rectangular inlet 33c extending in the
widthwise direction, through which the sheet 3 is introduced into
the casing 33. The casing 33 also has a rear wall 33b formed with a
rectangular outlet 33d extending in the widthwise direction through
which the sheet is delivered out of the casing 33.
[0035] A generally rectangular attachment plate 34 protrudes
outwardly from each widthwise end of the front wall 33a of the
casing 33. Each attachment plate 34 is formed with a generally
circular attachment hole 34a. Further, a generally rectangular
receiving hole 38 is formed at the widthwise center and above the
inlet 33c in the front wall 33a for receiving a temperature sensor
41 described later in the receiving hole 38. The receiving hole 38
is penetrated through the front wall 33a. The temperature sensor 41
is one of the elements in a temperature sensing section 40 (FIG. 4)
of the temperature sensor unit 35.
[0036] Three positioning recesses 37 are formed around the
receiving hole 38 at positions corresponding to corners of an
isosceles triangle in the front wall 33a. That is, a first recess
is positioned at one widthwise side of the receiving hole 38, a
second recess is positioned at another widthwise side thereof, and
a third recess is positioned below and a center of the receiving
hole 38. In other words, the three positioning recesses 37 are not
in line. Each positioning recess 37 has a conical shape for
receiving therein each positioning pin 50 described later as shown
in FIGS. 4 and 5.
[0037] The temperature sensor unit 35 has a support plate 36
described later fixed to the main casing 2, and the casing 33 is
detachably assembled to the support plate 36. That is, the support
plate 36 has fixing plates 39 each formed with an insertion hole
39a. Each attachment hole 34a of the attachment plate 34 is aligned
with each insertion hole 39a of each fixing plate 39, and a screw
(not shown) is threadingly engaged with each attachment hole 34a
and the insertion hole 39a for detachably fixing the casing 33 to
the support plate 36. Thus, the thermal fixing unit 32 is
detachably assembled to the main casing 2.
[0038] As shown in FIGS. 1 and 2, a rear cover 30 is provided at a
rear side of the main casing 2. A hinge 29 is provided at a rear
lower side of the main casing 2, and the rear cover 30 is pivotally
supported to the main casing 2 through the hinge 29. The rear cover
30 is pivotally movable in a frontward/rearward direction to
provide a closed state (FIG. 1) and an open state (FIG. 2). For
attaching or detaching the thermal fixing unit 32 to and from the
main casing 2, the rear cover 32 is opened. Upon completion of the
attachment, the rear cover 32 is closed. An attachment/detachment
path is provided between a rear wall of the main casing 2 and the
temperature sensor unit 35 for attaching and detaching the thermal
fixing unit 32 to and from the temperature sensor unit 35.
[0039] FIG. 2 shows a state for detaching the thermal fixing unit
32 from the main casing 2. In this state, the thermal fixing unit
32 is moved rearwardly as indicated by an arrow in FIG. 2. Because
the temperature sensor unit 35 is positioned in front of the
thermal fixing unit 32, that is, at a side opposite to the
attachment/detachment path of the thermal fixing unit 32, no
mechanical interference occurs between the temperature sensor unit
35 and the thermal fixing unit 32 during detachment of the thermal
fixing unit 32. Thus, the thermal fixing unit 23 can be smoothly
detached from the main casing 2 without any damage to the thermal
fixing unit 32 and to the temperature sensor unit 35.
[0040] The heat roller 22 is disposed in the casing 33 and is made
from a metal such as aluminum. The heat roller 22 is formed into a
hollow cylindrical shape by drawing. The heat roller 22
accommodates therein a heater 26 such as a halogen heater extending
in an axial direction of the heat roller 22. The heater 26 releases
heat upon power supply from a power source (not shown) for heating
the heat roller 22. More specifically, the heater 26 is subjected
to ON/OFF control from a CPU (not shown) in accordance with the
detection of a temperature at a surface of the heat roller 22 by a
temperature sensor 41 described later, thereby maintaining the
surface of the heat roller 22 at a predetermined thermal fixing
temperature.
[0041] The pressure roller 23 is also disposed in the casing 33 and
is positioned immediately below the heat roller 22 interposing
therebetween a sheet convey path. The pressure roller 23 includes a
metal roller shaft and an elastic roller portion formed thereover
in pressure contact with the heat roller 22. The transport roller
25 is supported at a rear wall of the casing 33, and includes a
pair of rollers arrayed vertically and positioned at the outlet
33d.
[0042] A discharge roller 27 is disposed downstream of the
transport roller 25, and a discharge tray 28 is provided at an
uppermost portion of the main casing 2. Further, a sheet discharge
sensor 24 is disposed at the rear cover 30 and is positioned
adjacent to and downstream of the transport roller 25. The sheet
discharge sensor 24 has an actuator rendered ON upon abutment of
the sheet 3 and rendered OFF when the sheet does not abut the
actuator in order to detect the discharge of the sheet 3.
[0043] The toner image carrying sheet 3 is conveyed from the
process device 10 into the inlet 33c. Then, the toner image is
thermally fixed to the sheet 3, while the sheet 3 is pressedly and
heatedly nipped between the heat roller 22 and the pressure roller
23. The sheet then passes through the outlet 33d and is discharged
onto the discharge tray 28 through the transport roller 25 and the
discharge roller 27.
[0044] The temperature sensor unit 35 is disposed in front of the
thermal fixing unit 32, and includes the temperature sensing
section 40 and the support plate 36 for supporting the temperature
sensing section 40 to the main casing 2. The support plate 36 is of
an elongated plate shape extending in the widthwise direction of
the sheet 3. The support plate 36 has a lower portion formed with
an inverted U-shaped opening 36a for allowing the sheet 3 to pass
therethrough. As described previously, each fixing plate 39 is
provided at each widthwise end of the support plate 36. The
generally circular insertion hole 39a is formed at a center portion
of each fixing plate 39. Further, two fixing holes 39b are formed
at widthwise outer side of each insertion hole 39a. Each fixing
plate 39 is positioned rearwardly of the support plate 36 to
provide a stepped portion, so that each attachment plate 34 of the
casing 33 can be easily abutted against each fixing plate 39.
[0045] Screws (not shown) are inserted through the respective
fixing holes 39b for fixing the fixing plates 39 to the main casing
2. Thus, the support plate 36 is fixed to the main casing 2, i.e.,
the temperature sensor unit 35 is fixed to the main casing 2. As
described above, because the casing 33 of the thermal fixing unit
32 is detachably fixed to the support plate 36, the thermal fixing
unit 32 can be detachably fixed to the temperature sensor unit 35
and to the main casing 2. The support plate 36 is positioned in
front of the casing 33, so that the toner image carrying sheet 3
will be introduced into the inlet 33c of the casing 33 after the
sheet 3 has passed through the inverted U-shaped opening 36a.
Incidentally, the temperature sensor unit 35 can be detached from
the main casing 2 by releasing the screws extending through the
fixing holes 39b from the main casing 2.
[0046] As shown in FIG. 3, the temperature sensing section 40 is
provided on a temperature sensing plate 40a having a rectangular
shape and positioned at the widthwise center and an upper portion
of the support plate 36. As shown in FIG. 4, the temperature
sensing section 40 includes the temperature sensor 41, a sensor
holder 43 for holding the temperature sensor 41, and a sensor
casing 44 for resiliently supporting the sensor holder 43.
[0047] The temperature sensor 41 includes a light receiving portion
45 for detecting an infrared radiation released from an outer
peripheral surface of the heat roller 22, and a conduit 42 for
introducing the infrared radiation into the light receiving portion
45. The light receiving portion 45 is provided by a non-contact
type infrared radiation sensor positioned spaced away from the
outer peripheral surface of the heat roller 22 in a non-contacting
fashion in order to detect a surface temperature of the heat roller
22. The infrared radiation sensor 45 is of a thermoelectromotive
force type thermopile where a thermopile element, which is an
integrated thermocouple is used.
[0048] To be more specific, the light receiving portion 45 includes
a can case 48 which receives infrared radiation released from the
outer peripheral surface of the heat roller 22, and the thermopile
elements 46 that detects infrared radiation received by the can
case 48. The can case 48 has a cylindrical shape and has a
detection window 47 through which an incident infrared ray passes.
The detection window 47 is provided at an end of the can case 48
and has a rectangular shape with a predetermined area capable of
providing a predetermined angle of field of view to detect the
infrared radiation. Further, the detection window 47 is provided
with an optical filter that allows specific infrared radiation
having wavelength of not less than 5 .mu.m to transmit
therethrough. That is, the infrared radiation having wavelength of
less than 5 .mu.m is absorbed by a water vapor. Therefore, the
filter prevents the infrared radiation having wavelength of less
than 5 .mu.m from being transmitted therethrough in order to avoid
degradation of the detection accuracy dependent on variation in
amount of infrared radiation due to variation in amount of water
vapor. The thermopile element 46 has a rectangular shape and
positioned at opposite end of the can case 48 in confronting
relation to the detection window 47.
[0049] Incidentally, the angle of field of view is a view angle
capable of providing 50% sensitivity with respect to a detection
sensitivity by the thermopile element 46 when an object to be
detected is disposed in front of the thermopile element 46 through
the detection window 47. For example, the angle of field of view of
.+-.26.degree. or .+-.60.degree. is available in the light
receiving portion 45.
[0050] The conduit 42 is in a hollow cylindrical shape and
insertable into the receiving hole 38 of the casing 33. The conduit
42 has a metallic inner peripheral surface serving as a reflection
surface for reflecting infrared radiation. When the thermal fixing
unit 32 is assembled to the main casing 2, one open end 42a of the
conduit 42 is inserted into the receiving hole 38 of the casing 33,
while another open end of the conduit 42 is assembled to the
detection window 47 of the can case 48 of the light receiving
portion 45. The one open end 42a is spaced away from the outer
peripheral surface of the heat roller 22 by a predetermined
distance. The inner reflection surface of the conduit 42 is formed
from a metal such as aluminum, silver and gold, those providing
reflection rate of the infrared radiation of not less than 80%.
Gold is preferable since its reflection rate of the infrared
radiation is sufficiently high such as about 98%.
[0051] As shown in FIGS. 4 through 6, the sensor holder 43 includes
a generally rectangular base plate 49, three positioning pins 50
and three spring securing projections 51, those integral with each
other. The base plate 49 has a central portion where the
temperature sensor 41 is insertedly held in a direction
perpendicular to the base plate 49, that is, in the
attachment/detachment direction of the thermal fixing unit 32.
[0052] Each positioning pin 50 extends toward the thermal fixing
unit 32 from the base plate 49 and is positioned to be engaged with
corresponding recess 37 of the casing 33 when the thermal fixing
unit 32 is assembled to the main casing 2. That is, one positioning
pin 50 is positioned obliquely above the temperature sensor 41,
second positioning pin 50 is positioned oppositely obliquely above
the temperature sensor 41, and third positioning pin 50 is
positioned vertically below the temperature sensor 41, so that
these pins 50 define an imaginary triangle around the temperature
sensor 41. Each tip end of each positioning pin 50 is a conical
shape for facilitating engagement with the corresponding
positioning recess 37. Each spring securing projection 51 protrudes
from the base plate 49 in a direction opposite to the protruding
direction of each positioning pin 50, and in line therewith.
[0053] The sensor casing 44 includes a spring support plate 53 four
engaging legs 56, and three compression springs 52. The spring
support plate 53 is provided on the temperature sensing plate 40a,
and has an outer rectangular contour smaller than that of the
temperature sensing plate 40a. Three recesses 54 serving as spring
seats are formed on a surface of the spring support plate 53 at
positions corresponding to the spring securing projections 51. Each
compression spring 52 has one end disposed over each spring
securing projection 51, and another end seated on each spring seat
recess 54.
[0054] The four engaging legs 56 protrude from the spring support
plate 53 toward the thermal fixing unit 32. These engaging legs 56
have length equal to one another, and each engaging leg 56 is
positioned in alignment with each corner of the base plate 49 as
shown in FIG. 6. Further, each engaging leg 56 has each free end
provided with a locking pawl 55 for engagement with each corner
portion of the base plate 49. Upon engagement, distances between
the spring support plate 53 and each corner portion of the base
plate 49 are equal to one another.
[0055] Thus, for assembling the temperature sensing section 40, the
temperature sensor 41 is fixed to the base plate 49 of the sensor
holder 43. Then, the base plate 49 is positioned within the four
engaging legs 56 while each one end of each compression spring 52
is disposed over each spring securing projection 51 of the sensor
holder 43 and each other end of each compression spring 52 is
seated on each recess 54. Because of the biasing force of the
compression springs 52, the sensor holder 43 is urged in a
direction away from the spring support plate 53, so that each
corner portion of the base plate 49 is brought into engagement with
each locking pawl 55. Thus, the sensor holder 43 is resiliently
supported in the sensor casing 44.
[0056] In a case where the thermal fixing unit 32 has been removed
from the main casing 2 as shown in FIG. 5, the sensor holder 43 is
urged in a direction away from the spring support plate 53 by the
biasing force of the compression springs 52, so that each corner
portion of the base plate 49 is engaged with each locking pawl 55.
In this state, the base plate 49 is resiliently held in the sensor
casing 44 and extends in a direction parallel to the spring support
plate 53. Thus, the temperature sensor 44 and each positioning pin
50 are directed in the attachment/detachment direction of the
thermal fixing unit 32.
[0057] For assembling the thermal fixing unit 32 to the main casing
2, the rear cover 30 is opened as shown in FIG. 2, and the thermal
fixing unit 32 is inserted frontwardly toward the main casing 2. By
the insertion, the temperature sensor 41 fixed at the sensor holder
43 is brought into insertion into the receiving hole 38 of the
front wall 33a of the casing 33, and as a result, the front open
end 42a of the conduit 42 is positioned in confrontation with the
outer surface of the heat roller 22 by a predetermined distance as
shown in FIG. 4.
[0058] In this state, as shown in FIG. 4, the each positioning pin
50 of the sensor holder 43 is brought into abutment with each
positioning recess 37 formed at the front wall 33a. The sensor
holder 43 is moved, within the sensor casing 44, toward the spring
support plate 53 against the biasing force of the compression
springs 52 because of the reaction force from the positioning
recess 37. Finally, the sensor holder 43 is stopped at a
predetermined posture. Consequently, a posture of the temperature
sensor 41 is fixed to thus fix the distance and orientation of the
temperature sensor with respect to the heat roller 22.
[0059] With this arrangement, relative position between the heat
roller 22 and the temperature sensor 41 can be maintained in a
constant fashion even after disassembly and assembly of the thermal
fixing unit 32 from and to the main casing 2. Because the distance
and orientation of the temperature sensor 41 with respect to the
heat roller 22 can be accurately provided each time the thermal
fixing unit 32 is assembled to the main casing 2, surface
temperature of the heat roller 22 can be precisely detected with
high repeatability thereby enhancing detection accuracy. This
advantage is particularly important for the thermopile type
infrared radiation sensor where its light receiving portion 45 is
subjected to severe requirements in distance and orientation with
respect to the object to be detected.
[0060] Further, with this arrangement, relative position between
the heat roller 22 and the temperature sensor 41 can be easily
fixed by the simple arrangement, i.e., by the engagement between
the positioning pins 50 and the positioning recesses 37. Moreover,
because the base plate 49 is resiliently supported by the
compression springs 52 each corresponding to each positioning pin
50, and because three positioning pins 50 and associated three
positioning recesses 37 are not in line, but offset from each other
in a triangular fashion, the base plate 49 can be held at a desired
orientation upon engagement between the pins and recesses without
any rattling. Thus, stabilized positioning of the temperature
sensor 41 results.
[0061] Then, screws are threadingly inserted through the attachment
hole 34a of the attachment plate 34 of the casing 33 and through
the insertion hole 39a of the fixing plate 39 of the support plate
36 fixed to the main casing 2 to fixedly secure the thermal fixing
unit 32 to the main casing 2.
[0062] After the thermal fixing unit 32 is assembled to the main
casing 2, as shown in FIG. 4, the open end 42a of the conduit 42 is
received in the receiving hole 38 of the casing 33, and relative
position between the open end 42a and the heat roller 22 can be
fixed. The infrared radiation emitted from the surface of the heat
roller 22 is directed to the detection window 47 of the light
receiving portion 45 through the reflection at the inner peripheral
reflection surface of the conduit 42, and is detected by the
thermopile element 46. Because the light receiving portion 45 is
spaced away from the surface of the heat roller 22 through the
interposition of the conduit 42, durability of the light receiving
portion 45 can be enhanced. Further, a surface temperature of the
heat roller 22 can be detected at high sensitivity because the
infrared radiation from the heat roller 22 can be trapped by the
open end 42a of the conduit 42 and the trapped infrared radiation
can reach the light receiving portion 45 as a result of the
reflection at the reflection surface of the conduit 42.
[0063] Furthermore, because the temperature sensor 41 is composed
by the non-contact type infrared radiation sensor positioned spaced
away form the surface of the heat roller 22, prolonged service life
of the sensor can result with a lesser damage. On the other hand,
the heat roller 22 and the pressure roller 23 of the thermal fixing
unit 32 will be worn due to mutual pressure contact as a result of
long term operation, and must be replaced by new heat roller and
new pressure roller. In this case, only the thermal fixing unit 32
can be disassembled from the main casing 2 without disassembly of
the temperature sensor unit 35 to save a cost. In this disassembly,
the temperature sensor unit 35 is not on the attachment/detachment
path of the thermal fixing unit 32. Therefore, no mechanical
interference occurs between the temperature senor unit 35 and the
thermal fixing unit 32, thereby further prolonging service life of
the temperature sensor 41.
[0064] Since the temperature sensor unit 35 is fixed to the main
casing 2 by screws (not shown) inserted through the fixing holes
39b, the temperature sensor unit 35 can be removed from the main
casing 2 by unfastening the screws when the temperature sensor 41
must be replaced by a new temperature sensor due to any damage or
expiration of span of service life.
[0065] Thus, in the laser printer 1, the sheet 3 is nippingly and
heatedly conveyed between the pressure roller 23 and the heat
roller 22, during which the surface temperature of the heat roller
22 is detected by the temperature sensor 41 so as to perform ON/OFF
control to the heater 26 based on the detected temperature in order
to maintain a desired fixing temperature.
[0066] A thermal fixing device according to a second embodiment of
the present invention will be described with reference to FIG. 7
wherein like parts and components are designated by the same
reference numerals as those shown in the first embodiment. In the
first embodiment three spring securing portions 51 protrude from
the base plate 49 and three compression springs 52 and three spring
seats 54 are provided. On the other hand, in the second embodiment,
only one spring securing portion 151 having a diameter greater than
that of the spring securing portions 51 protrudes from a center
portion of a base plate 149. Further a spring support plate 153 is
formed with a single spring seat 154 and a single compression
spring 152 is interposed between the spring seat 154 and the single
spring securing portion 151. With this arrangement, the sensor
holder 43 can be resiliently supported in a manner similar to that
of the first embodiment.
[0067] FIG. 8 shows a thermal fixing device according to a third
embodiment. A temperature sensor 241 does not provide a conduit 42
of the foregoing embodiments, and a sensor cover 257 is pivotally
supported to the main casing 2 by a pivot shaft 260 for closing the
detection window 47 of the light receiving portion 45 when the
thermal fixing unit 232 is moved away from the temperature sensor
241.
[0068] More specifically, the sensor cover 257 is in a bent shape
having a major arm section 258 adapted for covering the detection
window 47 and an abutment arm section 259 integral with the major
arm section 258. The major arm section 258 is directed vertically
because of its gravity when the major arm 258 completely covers the
detection window 47. A casing 233 has an outer arm 261 whose free
end is abuttable onto a free end of the arm section 259 when the
thermal fixing unit 232 is assembled to the main casing 2. The
casing 233 is formed with an elongated hole 262 opened at its front
end face for receiving therein the major arm section 258 when the
sensor cover 257 is pivotally moved by the forward movement of the
outer arm 261.
[0069] When the casing 233 is moved away from the temperature
sensor 241 as the thermal fixing unit 232 is removed from the main
casing 2, the major arm section 258 of the sensor cover 257 is
suspended vertically downwardly because of its gravity so that the
major arm section 258 covers the detection window 47 as shown by a
solid line in FIG. 8. As a result, the detection window 47 is
protected against dirt and damage during replacement of the thermal
fixing unit 232. Thus, the temperature sensor 241 can perform
accurate temperature detection for a long duration.
[0070] In assembly of the thermal fixing unit 232 to the main
casing 2, the outer arm 261 of the casing 233 pushes the free end
portion of the abutment arm section 259 frontwardly as shown by a
broken line in FIG. 8, so that the major arm section 258 is
pivotally moved in a clockwise direction in FIG. 8 about the pivot
shaft 260. As a result, the major arm section 258 is gradually
directed horizontally and is inserted into the elongated hole 262
thereby opening the detection window 47 capable of confronting the
heat roller 22.
[0071] FIG. 9 shows a thermal fixing device according to a fourth
embodiment which is a modification to the third embodiment. The
fourth embodiment employs a protection film 367 instead of the
sensor cover 257 of the third embodiment for protecting the
detection window 47. More specifically, a film feed section 365 for
feeding the protection film 367 is provided on a temperature
sensing plate 340a and at one side of the temperature sensor 41,
and a film take-up section 366 for taking up the film 367 is
provided on the temperature sensing plate 340a and at another side
of the temperature sensor 41. Thus, the protection film 367 is
bridged over the detection window 47 and between the film feed
section 365 and the film take-up section 366. The protection film
367 is made from a transparent material such as polyimide which
transmits infrared radiation therethrough.
[0072] In the film feed section 365, a film feed reel 368 winding
thereover a new elongated film is rotatably provided for unwinding
the new film 367. In the take-up section 366, a film take-up reel
69 is rotatably provided for taking-up the used film 367. The
take-up reel 369 is rotatable by a predetermined numbers by a drive
motor (not shown). The film 367 is always bridged over the
detection window 47. The drive motor is temporarily rotated at a
predetermined timing, for example, at the time of replacement of
the thermal fixing unit, so that a new area of the film 367 can be
positioned over the detection window 47 as a result of the
predetermined number of rotation of the take-up reel 369. Thus, the
detection window 47 can be protected for a long duration, to
provide accurate temperature detection for the duration.
[0073] While the invention has been described in detail with
reference to specific embodiments thereof, it would be apparent to
those skilled in the art that various changes and modifications may
be made therein without departing from the spirit and scope of the
invention.
[0074] For example, in the foregoing embodiments, the temperature
sensors detect the surface temperature of the heat roller 22.
However, surface temperature of the pressure roller 23 can be
detected instead of the detection of the surface temperature of the
heat roller, because these temperatures are closely related to each
other as a result of nipping contact with each other.
[0075] Further, in the foregoing embodiments, positioning recesses
are formed in the casing of the thermal fixing unit, and
positioning pins engageable with these recesses are provided at the
temperature sensor unit. However, these recesses can be formed in
the temperature sensor unit, and these pins can be provided at the
thermal fixing unit. Furthermore, numbers and positions of these
pins and recesses are not limited to the foregoing embodiments, but
can be modified depending upon intended orientation and use.
[0076] Further, in the foregoing embodiments, the non-contact type
infrared radiation sensor is used which is out of contact from the
surface of the heat roller. However, a contact type temperature
sensor such as a thermistor is also available.
* * * * *